Suspended layered energy absorbing material for vehicle arresting systems

ABSTRACT

Embodiments of the invention described herein thus provide systems and methods for arresting aircraft. In specific embodiments, the systems and methods can be useful in arresting light aircraft because they typically do not have the weight to penetrate available EMAS systems. The system is generally provided as a structure having a suspended layer of energy absorbing material. A lower portion of the system can have a lower strength, used as a method to suspend an upper, stronger/more highly energy absorbent portion of the system.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of U.S. Provisional Application Ser.No. 62/163,180, filed May 18, 2015, titled “Composite Layered EnergyAbsorbing Material for Vehicle Arresting Systems,” the entire contentsof which are hereby incorporated by reference.

FIELD OF THE DISCLOSURE

Embodiments of the present disclosure relate generally to vehiclearresting systems that are designed for installation at the end of arunway or other surface that is subject to potential vehicle overrun.Embodiments find particular use when installed at the end of an aircraftrunway and when used to arrest light aircraft.

BACKGROUND

Vehicle arresting systems are used as barriers at the end of runways todecelerate aircraft that overrun the end of the runway. These systemsare designed to predictably and reliably crush (or otherwise deform ordisplace) under the pressure of aircraft wheels. The materials used insuch a system are generally compressible, deformable, crushable, orotherwise able to be compressed, deformed, or crushed upon appropriateimpact. The materials are generally designed to have a low strength thatallows their crushing upon impact. During an arrestment, the wheels ofthe aircraft crush (or deform) the material. The depth of wheelpenetration into the material is dependent on the vertical load appliedby the material. The deceleration of the aircraft is dependent on thedrag load applied by the material. In most arresting systems, the maincore crushable material has isotropic properties which provide a fixedratio between the wheel penetration and deceleration for each aircraft.

Due to this ratio, traditional arresting systems may not be able todecelerate certain lighter aircraft in the desired or available overrunarea. For example, light aircraft may not have enough weight upon impactwith the vehicle arresting barrier to cause the wheels of the aircraftto sink deep enough into the barrier material or otherwise crush enoughof the barrier for arrestment.

BRIEF SUMMARY

Embodiments of the invention described herein thus provide systems andmethods for arresting aircraft. In specific embodiments, the systems andmethods can be useful in arresting light aircraft because they typicallydo not have the weight to penetrate available EMAS systems. However, itshould be understood that the discloses systems and methods may work forany type of aircraft or vehicle, including commercial aircraft. Thesystem is generally provided as a structure having a suspended layer ofenergy absorbing material. A lower portion of the system can have alower strength/is weaker, which can be used as a method to suspend anupper, stronger/more highly energy absorbent portion of the system. Thisresults in less vertical resistance to penetration while still providinga large(er) force in the horizontal plane (drag load).

In one example, there is provided a vehicle arresting system layeredstructure that has at least one suspended upper portion of energyabsorbing material having a first strength, and a lower base portioncomprising a material of a second, lower strength than the material of afirst strength. The lower base portion can be a layer of a more easilycrushable material than the upper suspended portion. In some examples,the suspended upper portion comprises deformable material. In otherexamples, the suspended upper portion comprises crushable material.

There may be provided additional portions of material that decrease inenergy absorbing capabilities moving from the upper portion to the lowerportion. The suspended upper portion and the lower base portion comprisegradients within the structure. Furthermore, the gradients can extendbetween the suspended upper portion and the lower base portion andfurther extend between a foremost portion and a rearmost portion.

In other examples, the lower base portion includes one or more columnsof the material of a lower strength with one more voids therebetween.The material of a lower strength of the lower base portion can compriseone or more voids.

In use, there is provided a method for arresting an aircraft,comprising, installing a vehicle arresting system having any of theabove features at an end of a runway or other overrun area. Specificexamples may be installed at an airport or on a runway that is accessedby lightweight aircraft.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic view of an aircraft wheel deforming a layeredstructure arresting system.

FIG. 2 shows a schematic view of an aircraft wheel crushing a layeredstructure arresting system.

FIG. 3 shows a schematic illustrating layers of high to low strengthmaterials.

FIG. 4 shows a schematic illustrating an alternate embodiment of layersof high to low strength materials.

FIG. 5 shows a schematic of a structure having a gradient of strengththerethrough.

FIG. 6 shows a schematic of a structure having further gradients ofmaterial strengths.

FIG. 7 shows a schematic illustrating an upper layer of high-strengthmaterial and lower layer made of a combination of low strength materialand voids.

FIG. 8 shows a schematic illustrating a lower portion material havingvoids therein.

FIG. 9A shows a schematic of an example of a typical EMAS high-strengthmaterial.

FIG. 9B shows a schematic of a layered structure and loads applied inuse.

DETAILED DESCRIPTION

Embodiments of the present invention provide a suspended layer of energyabsorbing material used for vehicle arresting systems. The compositematerial is particularly designed for arresting light aircraft in anoverrun event. As used herein, “light aircraft” generally means aircraftthat are lighter than traditional wide-body or twin-aisle aircraft usedfor long haul flights. The term “light aircraft” includes but is notlimited to business jets, microjets, cessnas, regional airliners,commuter aircraft, short-haul aircraft, or civil aviation aircraft.Light aircraft are generally lighter than traditional commercialpassenger aircraft.

In a overrun situation, the wheels of an aircraft may not have a loadthat can penetrate a traditional arresting system in the vertical loaddirection in the way that the heavy load of a larger aircraft would.Wheels of light aircraft may not sink deep enough in a traditionalvehicle arresting barrier system. Additionally, effective arresting ofan overrun light aircraft may benefit from a shallow arresting system,which can help avoid propeller strikes.

Accordingly, the suspended layer of energy absorbent material describedherein is designed to provide additional drag load in the horizontaldirection. The general intent is to accommodate/apply a largerhorizontal component of force in the arresting process, whileeliminating some of the required vertical load required for crushing ofthe barrier material. The result is that wheels of a light aircraft areallowed to sink deeper into the lower layer of the arresting system, butan appropriate drag load is still provided by the upper layer.

The inventors have thus provided an arresting system that has theability to vary the drag and vertical load of the system. This can allowfor better arresting in a shorter overrun distance. This can also allowfor using the same area to arrest vehicles overrunning the runway athigher speeds (e.g., current engineered materials arresting systems(EMAS) are designed for exit speeds up to 70 knots).

The improved system 10 is generally provided with a suspended layer,resulting in more than one layer of varied material strength. A lowerbase portion of the system generally has a lower strength/is weaker thanan upper portion of the system. By providing a lower strength materialat the lower portion of the system, there is less vertical resistance topenetration. The practical effect of this design is that vehicle wheels,upon penetration of the upper/stronger portion, penetrate/crush/can bestopped by the drag load applied by the upper portion. A schematic ofthis effect is provided by FIG. 9B, described in more detail below. Asshown in this and other figures, because of the low strength lowerportion, the amount of wheel penetration is such that application of thedrag load from the upper layer (illustrated by horizontal arrows 80) canbe in line with the aircraft axle. Only the upper layer(s) apply/appliesthe drag load in line with the aircraft axel. The lower base layer issimply present in order to suspend the upper layer; it is not intendedto add any strength/drag load to the system.

Other EMAS systems that have experimented with different strengths ofmaterials have provided the denser/stronger material at the bottom and alighter/weaker material as the upper/top layer. The general theorybehind such systems is that they must be capable of stopping large,heavy aircraft and need to have the majority of the system made of thehigh-strength material. However, the wheels of light aircraft do notalways penetrate deep enough into the denser/stronger material at thebottom. The present inventors thus sought to provide a system that iscapable of stopping light aircraft of lower weight up to largecommercial aircraft within a shorter EMAS bed. The prior art systems ofproviding lighter material on top have only allowed lightweight aircraftto penetrate the top layer, but not penetrate deeply enough into thehigh-strength lower layer. The system described herein, with a lowerlayer suspending an upper layer of higher strength/higher energyabsorbent characteristics, allows for the wheel of an aircraft topenetrate the EMAS system with the vertical load typically required by alower strength material but still providing the drag load of a higherstrength material.

In general, the vehicle arresting systems described herein provide atleast one suspended upper portion/layer of a compressible material thatis supported by a lower base portion or area. The lower base layer orportion of material generally has lower energy absorptioncharacteristics than the suspended layer. In other words, the suspendedlayer is a more highly energy absorbent material that is suspended by alower material of a lesser or lower energy absorption capability thanthe layer directly above or vertically adjacent thereto. The vehiclearresting system may be an elevated panel or plane of compressiblematerial, with the compressible material having a plurality of layerswith energy absorption capabilities that decrease relative to the panelor layer directly above said panel (when moving down the vertical axisfrom the upper to lower most layer).

In one example, the system 10 provides two or more horizontal layers 12,14 of crushable (or deformable) material. The upper suspended layer 12is designed as having a higher strength than the lower base layer 14.The layers may be horizontal panels of crushable (or deformable)material(s). Multiple layers are illustrated by FIGS. 1-4. In otherexamples, the system 10 may provide a gradient 16 of strengths formedwithin a single structure 18 of material. The structure 18 may be ablock, a gradient system, or any other appropriate compilation ofmaterial. Various types of gradients are possible within the material,as described in more detail below. Gradients are illustrated by FIGS.5-6. In another example, the system 10 may provide a higher strengthupper suspended layer 12 with support columns 20 forming the lower baselayer, having voids 22 positioned therebetween. An example of thisembodiment is shown by FIG. 7. In a further example, a lower portion 24of the material may be provided with varying sized voids 26, renderingthe material at the lower portion 24 weaker than the material at theupper portion 28. An example of this is illustrated by FIG. 8. All ofthese options are described in more detail below. Any of the materialsdescribed herein may be used for any of the layers, gradients, orportions. The layers, gradient, or portions of the material may all bereferred to as a “layered structure,” even if distinct and separatelayers are not specifically provided.

Each of these layers, gradients, or portions of the layered structurematerial is designed for the arresting performance of the system, butthey may provide protection in addition to arresting performance. Forexample, a stronger more dense upper layer may permit vehicles/personnelto traverse the EMAS system, whereas if the system was made of only ofthe lower strength material, such travel would not be possible.

Examples of materials that may be used for any of the layers, portions,or gradients described herein include but are not limited to cellularcement, cellular cementitious material, polymeric foam, honeycomb, metalhoneycomb, macro particles, vermiculite, perlite, ceramics, foam glassand other isotropic or anisotropic crushable/deformable materials, orcombinations thereof. Each material can have different mechanical andphysical properties and geometry. Each material can be selected to tunethe desired properties of the overall structure.

One specific example of materials forming the layered structures may bea combination of a polymeric foam forming the lower layer and a metallichoneycomb forming the upper layer. The polymeric foam may have itsdensity/strength varied based on foam formation methods. In anotherspecific example, a low strength honeycomb layer may support a layer ofcellular cement or polymeric foam. In a further example, a lowstrength/density polymeric foam may be used to support an upper layer ofcellular cement. Other combinations of materials and strengths arepossible and considered within the scope of this disclosure.

The materials may be selected to provide the desired strength ratios. Inone example, a drag to vertical load ratio may reach 1:1. It may bepossible to get the ratio even higher than 1:1, and higher drag tovertical loads are desirable. For example, the ratio may be 2:1, 5:1, or10:1. The general goal is that for every pound of drag, there be a equalor smaller amount of vertical load required to penetrate into thesystem. It is desirable that the resistance of the aircraft wheelrequired to travel through the high strength material in the verticaldirection be minimized, and that horizontal resistance (drag) beingapplied to the wheel be great.

The layered structure may be comprised of different materials. Forexample, FIGS. 1 and 2 show a lower layer 14 of weaker materialpositioned under an upper layer 12 of a higher strength material. Thematerial itself may be the same material with differentphysical/mechanical properties. Alternatively, different types ofmaterial may be provided to form each layer 12, 14. In FIG. 1, the upperlayer 12 is a deformable, strong material. The lower layer 14 is weaker,crushable material. In this example, the lower portion is thicker (orotherwise forms more of the bulk of the system) than the upper portion.

The system (both upper and lower layers) may be coated in a coating,film or shell, collectively referred to as a “shell.” This shell can beprovided to protect the core energy absorbing material from the effectsof weathering/jet blast. The shell may be designed to shear and/or tear,allowing the wheel to penetrate into the core material. The shell may beelastic in nature, allowing it to deform and elongate (but not tear orshear) such that it deforms enough to allow the wheel to crush/deformthe core material. The core can be crushed and pressed and moved uponpressure, and the shell can elongate and deform to allow the wheel tomove through the material, while containing the upper and lower layers,and preventing them from fracturing into pieces. In another example, theupper layer 12 may function like an elastic coating. For example, it maybe an elastic sprayable polymer. The upper layer 12 can deform upontouch but does not lose its integrity. The lower layer 14, however, canbe caused to crush or otherwise deform beneath the upper layer 12. Inuse, the wheel “W” penetrates the lower layer 14 without actuallycontacting the lower layer directly. The coating 12 in this examplefunctions to contain the core of the lower/upper layers 14.

In FIG. 2, the upper layer 12 is a layer of a strong, crushable materialand the lower layer 14 is a layer of a weaker, crushable material. Thesematerials may be the same materials, modified separately as describedbelow in order to alter their respective strengths. Alternatively, thesematerials may be completely different materials having differentstrengths that are layered upon one another. As illustrated, theaircraft wheels W are allowed to crush both layers 12, 14 during contactand the arrestment process.

For example, if the material used is polymeric foam, it is possible toalter the density/strength of the foam. This may done by varying cellalignment for different portions of the structure. In another example,this may be done by injecting voids into the foam in the form of airbubbles in order to weaken the lower portion areas of the foam.

Additionally or alternatively, one or more chunks of lighter materialmay be mixed into the foam or other material that forms the lowerportion of the system. Additionally or alternatively, particle sizes ofvarious materials used may be varied to change densities of theplayers/portions.

FIG. 3 illustrates a structure comprised of multiple layers, each withdiffering energy absorption characteristics. Each layer, plane or zonehas a specified strength that generally differs from one or more layers,planes or zones thereabove. The upper most layer 50 has the higheststrength, with the layers therebelow decreasing in strength. Forexample, the next layer 52 has a high strength (as compared to layer50). The next layer 54 has a medium strength (again, comparatively). Thenext layer, the lowermost layer 56, has a comparatively low strength.Although an example with four layers is shown, it should be understoodthat more or fewer layers may be provided. It is also possible that thelayer strengths need not vary greatly or substantially with respect oneanother. Small strength steps are possible and considered within thescope of this disclosure.

Additionally, an alternate example may be a high/low/high/lowembodiment. In this example, the upper most layer may have a highstrength, the next layer may have a low strength, the next layer downmay have a high strength, and the lowermost layer may have a lowstrength. The general concept is providing alternating of layerstrengths.

In any of the layer examples, it is possible for the layers to be bondedor adhered to one another using any appropriate EMAS technique. Adhesiveor high friction are examples only. In another example, it is possiblefor the layers to be stepped or laid on top of one another. In anyoption, the layers may then be contained by a separate containmentsystem. Exemplary containment systems are shown and described by many ofthe present assignee's pending applications and issued patents.Alternatively, the containment system could be a sprayable covering, aflame-resistant coating, a weather-resistant coating or any otherappropriate outer layer. These securement/containment system options maybe used in any of the examples described herein.

FIG. 4 illustrates an alternate embodiment in which the specifiedstrength layers have varying heights. In the example shown, theuppermost, highest strength layer 50 is shown as thicker than the lowerlayers. Alternatively, it is possible for the uppermost, higheststrength layer 50 to be thinner than the lower layers, such that thehigh, medium, and/or low strength materials provide a larger portion ofthe barrier material.

FIG. 5 illustrates a gradient material 16 formed as a structure 18. Asdiscussed above, the structure may be a block, a gradient system, or anyother appropriate compilation of materials. Rather than having two ormore separate layers bonded, this embodiment provides a single structure18 that has an increasing density moving upwards from the bottom towardsthe top face 40 of the structure or block, and the direction of arrow70. Considered a different way, there is a decreasing density movingdown through the structure or block, from the top towards the bottomface 42. The gradient of energy absorbing ability decreases from theupper most plane to the lower most plane. This gradient of energyabsorbing ability may be provided by any of the above-describedmodifications to a material. It may be referred to as a top-to-bottomgradient.

FIG. 6 illustrates a gradient material 30 formed as a structure 18. Asdiscussed above, the structure may be a block, a gradient system, or anyother appropriate compilation of materials. In this example, sections ofmaterial are oriented to have a gradient of energy absorbingcapabilities that increases from lower most to uppermost, as well asfrom foremost to rear most of the system. More specifically, a lowerstrength material is provided at a front portion 32 of the structure. Ahigher strength material is provided at a rear portion 34 of thestructure. The material therebetween 36 is generally formed as agradient of gradually increasing strength. The gradually increasingstrength of this section moves from a lower portion of the structure toan upper portion of the structure, as well as from a front portion to arear portion. This example provides an energy absorbent material withthe internal energy absorbing characteristics varying from the lowestpoint to the uppermost point and varying from the frontmost point to therearmost point.

Although shown as a gradient, it is also possible to provide this effectusing various structures, blocks, or layers. For example, the frontmostportion, structure or block may be provided having a lower energyabsorption ability (i.e., a weaker strength) and rear most and higherportions, structures, or blocks may be provided having a higher energyabsorption ability (i.e., a stronger strength).

FIG. 7 illustrates an embodiment having an upper layer 12 of a highstrength and a lower portion 60 that is formed of support columns 20 oflow strength material with voids 22 interspersed therebetween. The voids22 may be actual openings in which no material is present. In otherexamples, the voids 22 may be formed of material having an even lowerstrength than the low strength support columns 20. The result is that ahighly energy absorbent material forms the uppermost layer and issupported by columns of lower energy absorbent material with voidsbetween the columns.

FIG. 8 illustrates a schematic of a configuration in which the lowerportion 24 is made to have lower energy absorption abilities through theintroduction of voids 26. The voids 26 are illustrated as having varyingsizes and shapes. It should be understood however that the voids may allbe similarly sized and shaped. The voids may be formed using any of theabove-described methods or materials. Additionally, although the voidsare shown as circular, it should be understood that the shapes wouldgreatly vary depending upon the way that the voids are formed. Thegeneral effect of voids 26 is that the lower portion 24 of the materialhas a lower energy absorption capability.

This performance of the systems described herein is different thantraditional EMAS systems, which have isotropic material and systemproperties. A traditional EMAS system is illustrated by FIG. 9A. Thisexample is entirely a single strength material. By contrast, thesuspended layer structures disclosed can be designed to have a higherratio of drag load to vertical load. This is illustrated by FIG. 9B.Once the aircraft wheel W has penetrated into the system by deformation,crushing or by other method, the upper layer(s) would provide higherdrag load than a typical EMAS system with similar wheel penetration,leading to a more rapid deceleration of the aircraft during anarrestment. One purpose of this system is to be able to provide the dragload of a high strength material, but only require the vertical load ofa low strength material to penetrate into it. One benefit provided (vs.a typical EMAS) is that given the same vertical load, the aircraft willbe able to penetrate deeper into a suspended layer structure due to thelow strength lower layer, but receive the same amount of drag load as ifthe wheel had penetrated (the same depth) into the higher strengthmaterial.

Once the wheel has penetrated into the system by deformation, crushing,or by other method, the upper layer(s) provide a higher drag load than atypical EMAS system would for a similar weight aircraft, leading to amore rapid deceleration of the aircraft during an arrestment.

Some light aircraft have propellers or generally have limited groundclearance below, such that their wheels cannot penetrate certain depths.Accordingly, the structures described herein may be designed havingupper and lower layers of various heights, depending upon needs of theparticular runway or aircraft to be stopped. One non-limiting exampleincludes 5 to 12 inches of the material forming the barrier. In onespecific example, a 7 inch barrier may work with certain aircraft. Thebarriers described herein may include a ramp up portion, they may beinstalled directly above ground, and/or they may be installed slightlyor greatly below ground.

The varying strength layers allow the aircraft wheels W to penetrateinto the system with the force required by a low strength material, butto encounter the drag load that would typically be produced by a higherstrength material. The layer structure may be arranged in height andpositioning and strength/energy absorption based upon the desired degreeof penetration and resulting drag load for a specific size/weight of aspecific fleet mix. The drag and vertical loads can be tuned or modifiedto allow for better arresting in a shorter overrun distance and/or toallow for the same area to arrest vehicles overrunning the runway athigher speeds. Each layer can have different mechanical/physicalproperties and geometry and will be selected to tune to the desiredproperties of the overall structure.

Changes and modifications, additions and deletions may be made to thestructures and methods recited above and shown in the drawings withoutdeparting from the scope or spirit of the disclosure or the followingclaims.

What is claimed is:
 1. A vehicle arresting system layered structure,comprising: at least one suspended upper portion of energy absorbingmaterial having a first strength; and a lower base portion comprising amaterial of a second, lower strength than the material of a firststrength.
 2. The structure of claim 1, wherein the lower base portioncomprises a layer of a more easily crushable material than the uppersuspended portion.
 3. The structure of claim 1, wherein the suspendedupper portion comprises deformable material.
 4. The structure of claim1, wherein the suspended upper portion comprises crushable material. 5.The structure of claim 1, wherein the lower base portion is thicker thanthe upper portion.
 6. The structure of claim 1, wherein the lower baseportion is not as thick as the upper portion.
 7. The structure of claim1, further comprising additional portions of material that decrease inenergy absorbing capabilities moving from the upper portion to the lowerportion.
 8. The structure of claim 1, wherein the suspended upperportion and the lower base portion comprise gradients within thestructure.
 9. The structure of claim 8, wherein the gradients extendbetween the suspended upper portion and the lower base portion andfurther extend between a foremost portion and a rearmost portion. 10.The structure of claim 1, wherein the lower base portion comprises oneor more columns of the material of a lower strength and one more voidstherebetween.
 11. The structure of claim 1, wherein the material of alower strength of the lower base portion comprises one or more voids.12. The structure of claim 1, further comprising a protective shellaround the structure.
 13. A method for arresting an aircraft,comprising, installing the vehicle arresting system of claim 1 at an endof a runway or other overrun area.
 14. The method of claim 13, whereinthe vehicle arresting system is installed at an airport or on a runwaythat is accessed by lightweight aircraft.